Orosomucoid is a well-studied serum glycoprotein. It's amino acid sequence is known, and it possesses a single steroid receptor site with highest affinity for progesterone. It undergoes thermal polymerization in a reversible manner, a property which has not been examined in relationship to steroid binding. The physiological function of orosomucoid is unclear, but recent work has indicated important roles for orosomucoid in lipid clearance and the sequestering of drugs. Further, it appears that orosomucoid may be a steriod receptor protein normally found in the membranes of T and B lymphocytes which is released following proteolytic scission from 52,000 to 41,800 molecular weight. It is the intent of this proposal to study in detail the chemical nature and topography of the progesterone binding site in orosomucoid, and thermodynamic aspects of the binding process. The results will be related to the self-associative properties of the orosomucoid molecule. The proncipal methodologies to be used include ESR and immunoaffinity chromatography.